Field of the Invention
The present invention relates to an element substrate, a printhead, and a printing apparatus.
Description of the Related Art
Conventionally, it has been necessary to apply a stable voltage to a heater in order to achieve stable discharge characteristics in an inkjet printhead that discharges ink from a plurality of discharge ports using thermal energy. In an element substrate for a printhead, a plurality of heaters, and a plurality of driving elements in correspondence with the plurality of heaters are arranged. A driving element is configured by a field-effect transistor, and drives a heater by switching. When a plurality of such heaters are simultaneously driven, a large current flows to a ground wiring and a drive power supply wiring supplying power to the heaters. The occurrence of electromagnetic noise due to inductive coupling between the ground wiring and the drive power supply wiring on the rising edge and the falling edge of the supply of such a large current becomes a problem.
A logic circuit, other than a heater, that receives and processes high-speed print data is disposed in the element substrate of a printhead. For this reason, there is the possibility that a logic circuit malfunction will occur when electromagnetic noise due to the foregoing inductive coupling occurs in a ground wiring. Accordingly, a configuration in which, in the element substrate and the printhead, a heater ground wiring and a ground wiring for a logic circuit and the element substrate are separated is taken. By this, electromagnetic noise that occurs when a plurality of heaters are driven being transmitted to the ground wiring for the logic circuit and the element substrate is prevented, and the logic circuit malfunctioning is prevented.
In an element substrate for a printhead, substrate temperature control is being carried out in accordance with recent demand for improvements in image quality. In an element substrate for a printhead, there is variation in discharge speed and the amount of a droplet of ink discharged in accordance with the temperature. For this reason, if there is a temperature distribution depending on the position of the substrate temperature, the temperature distribution will result in image unevenness, and the image quality will decrease. As a method of correcting image temperature distribution, in Japanese Patent Laid-Open No. 2014-200972, for example, high image quality is realized by suppressing temperature unevenness in a substrate by a plurality of sub-heaters being disposed in an element substrate, and heating specific areas. Furthermore, because it is possible to heat a plurality of areas without increasing the number of terminals by mounting sub-heater driving elements in the element substrate, printing apparatus main body cost reduction can be realized.
When the plurality of sub-heaters are simultaneously driven, a large current on the order of A (amperes) flows. The length of wiring of the drive power supply wiring to the element substrate from a power circuit arranged on printing apparatus main body and the length of the wiring of a ground wiring become longer, and a parasitic inductance component becomes larger. Ringing occurs when a large current flows at a time of sub-heater driving to this parasitic inductance component. A potential difference between the ground wiring for a sub-heater and the ground wiring for an element substrate temporarily occurs due to such ringing. A field-effect transistor which is a driving element turns on by this potential difference, and as a result, a large current on the order of A (amperes) flows in the parasitic transistor, causing a malfunction of the driving element.